Details as previously stated, I use CS2 to finish off my shots but would suggest ImagesPlus 3 for all your pre CS2 operations.
http://www.mlunsold.com/
With ImagesPlus you can get both the Image proccessing software and Camera Control. You can purchase either the proccessing software or the camera control software alone or get both together, depending on your requirements, check out the website above for details.
You can also order direct from Mike Unsold.
I am not sure what Canon software comes with the 400D but there is a Camera Control Utility bungled with the software that allows long exposure shots to be taken, you can use it to also adjust your focus with timed shots and to setup a series of long exposures for DSO's etc.
Cheers